Stirling engine for an emission-free aircraft

ABSTRACT

Aircraft with an emission-free drive and method for emission-free driving of an aircraft. The aircraft includes a drive device structured and arranged to generate thrust, a lift device structured and arranged to generate lift, and a heat engine structured and arranged to convert thermal energy into kinetic energy to drive the drive device. The heat engine includes at least one flat-plate Stirling engine drivable by solar thermal radiation.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of U.S. application Ser. No.13/724,554 filed Dec. 21, 2012, which claims priority under 35 U.S.C.§119(a) of German Patent Application No. 10 2011 122 072.4 filed Dec.22, 2011, the disclosures of which are expressly incorporated byreference herein in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an aircraft with an emission-free drive and amethod for driving an aircraft.

2. Discussion of Background Information

Aircraft, for example, airplanes, generally have a drive device, forexample, a turbine or a propeller, which is driven, e.g., by an internalcombustion engine. In connection with the findings on global warming,efforts are currently being made to reduce the CO₂ discharge caused byoperating an airplane. For example, electric motors are being tested fortheir operational capability in aircraft, in particular in airplanes.The batteries necessary for this are not yet available according totoday's prior art. However, there are small flight demonstrators, suchas for example the electric flying Cri-Cri from EADS, which havedemonstrated the fundamental feasibility of electric flight with smallaircraft. Furthermore, there are solar aircraft, such as theSolarimpuls, which also render flight possible at night, in that solarenergy is converted by solar cells into electric current during the dayand is stored in batteries, which then drive an electric motor at night.

A solar-powered aircraft is known from WO 2008/121774 A2. To operate aheat engine in the form of a Stirling engine, a thermal battery with aheat storage medium is provided, as well as a solar thermal collectorprovided in the transparent fuselage. Since the aircraft is aligneddifferently to the sun during flight operation, a moveable parabolicreflector is provided with a thermal collector running centrally, whichtransports the heat to the thermal reservoir. Flat-plate Stirlingengines are known, for example, from U.S. Pat. No. 4,414,814, DE 42 16839 C1, WO 96/06274 or EP 2 258 947 A1.

SUMMARY OF THE EMBODIMENTS

Embodiments of the invention provide an aircraft with the lightestpossible drive with a reduced CO₂ discharge based on the operation.

Accordingly, embodiments are directed to an aircraft with anemission-free drive that includes a drive device for generating athrust, a lift device for generating a lift, and a heat engine forconverting thermal energy into kinetic energy for driving the drivedevice. At least one flat-plate Stirling engine that can be driven bysolar thermal radiation is provided as a heat engine. Moreover,embodiments are directed to a method for driving an aircraft thatincludes feeding of solar thermal energy to a flat-plate Stirlingengine, conversion of the thermal energy into kinetic energy by theflat-plate Stirling engine, and driving a drive device by the flat-plateStirling engine.

According to embodiments, an aircraft with an emission-free drive isprovided, which has a drive device for generating a thrust, a liftdevice for generating a lift and a heat engine for converting thermalenergy into kinetic energy for driving the drive device. At least oneflat-plate Stirling engine that can be driven by solar thermal radiationis provided as a heat engine.

A “flat-plate Stirling engine” is a Stirling engine in which a displacerwith intermittent control is provided. The displacer operates with verylow temperature difference, which is due to the fact that the system ofthe flat plate has a larger heat transfer surface in proportion to theworking volume. A surface also referred to as front wall is therebyheated, according to the present invention, in particular by solarinsolation. Flat-plate Stirling engines are suitable for convertingthermal energy, which is provided by the solar thermal radiation, intokinetic energy. Flat-plate Stirling engines can already be driven at lowtemperature differences, for example at a temperature difference ofapprox. 15°. Due to their active principle, flat-plate Stirling enginescan be realized with relatively light components. Due to the use of thesolar thermal radiation as a heat source, which is unavoidable for theoperation of the flat-plate Stirling engine, an emission-free drive,i.e., a drive with reduced CO₂ discharge, is possible.

The term “aircraft” also comprises airplanes and in particular mannedand unmanned airplanes. However, “aircraft” is also understood to meanairships as well as balloon vehicles.

The drive device is, for example, a propeller drive with one or morepropeller units.

The lift device comprises, for example, a body filled with alift-generating fluid of an airship or a balloon vehicle.

The lift device can also comprise a wing device with an airfoil sectionfor generating a lift (with correspondingly simultaneous thrust togenerate the necessary flow). The term “wing device” also comprises, forexample, the lift devices embodied or formed integrally with a fuselageconstruction in the case of all-wing aircraft.

According to embodiments, several flat-plate Stirling engines can beprovided, e.g., based on the flight direction next to one another or onebehind the other, or also arranged distributed at several points.

According to embodiments of the invention, the lift device comprises awing device with an airfoil section for producing a lift, in which theflat-plate Stirling engine is arranged in the wing device.

A flat-plate Stirling engine can thus be provided, which has a surfacethat is as large as possible exposed to solar thermal radiation.

Moreover, the flat-plate Stirling engine can optimally utilize thecross-sectional geometry of the airfoil section, which is also shown bythe following.

According to embodiments of the invention, the flat-plate Stirlingengine includes:

-   -   a working chamber filled with a working gas with a top and an        underside and a changeable working volume;    -   a displacer held in a moveable manner in the working chamber        between the top and the underside;    -   a regenerator arranged in the working chamber for collecting and        delivering thermal energy contained in the working gas;    -   a working piston connected to the working chamber for changing        the working volume;    -   an inertia element held in a rotatable manner;    -   a drive, connected to the inertia element, for driving the drive        device; and    -   a transmission device for the mechanically coupling connection        of the displacer and of the working piston with the inertia        element.

The working chamber is arranged in the lift device, and the working gascan be heated from a top of the lift device by the solar thermalradiation.

The alignment of the top to the solar thermal radiation results duringflight operation, since the top always points upwards and thus in thedirection of the solar insolation. The solar insolation, to put itsimply, causes a heating of the working gas in the region above thedisplacer, such that the working gas expands and presses the workingpiston outwards. Subsequently, a cooling takes place and thus acontraction of the working gas in the upper region and a new movement ofthe working piston occurs, whereupon a new step of heating and expandingbegins again. It is decisive hereby that the displacer transports theworking gas to and fro between the hot top and the cold underside inorder to achieve a quick cooling or heating of the working gas.

The inertia element is, for example, a propeller device of the drivedevice. The inertia element can also be embodied or formed as aflywheel.

Instead of the inertia element, a device can also be provided forconverting the linear movement into a rotational movement.

According to an alternative example, instead of the inertia element, adirect output is also provided via the linear movement of the workingpiston to generate a linear movement for a drive based thereon.

The transmission device has, for example, a first push-rod connection,which couples the displacer to a first pivot point on the inertiaelement, and a second push-rod connection, which couples the workingpiston to a second pivot point on the inertia element. The first pivotpoint is arranged on the inertia element offset by 90° in its rotationalangle position in the direction of rotation in front of the second pivotpoint.

The working piston is held in a moveable manner in a working cavity,wherein the working piston represents a moveable wall surface of theworking chamber.

According to a further embodiment of the invention, the working chamberis embodied or formed between the top of the wing and the underside ofthe wing. The displacer divides the working chamber into a first and asecond chamber region. The displacer is embodied or formed such that,with movement, it displaces working gas from the one into the otherchamber region. The top of the wing forms a first side of the flat-plateStirling engine with a first temperature and the underside of the wingforms a second side of the flat-plate Stirling engine with a secondtemperature. The second temperature is lower than the first temperature.

The first chamber region is an upper chamber region and the secondchamber region is a lower chamber region.

The working gas can be coolable, i.e., cooled from an underside of thelift device, e.g., on the underside of the wing. The wing device canhave a heat-conducting chamber wall in the region of the workingchamber, e.g., an aluminum sheet located, e.g., in the region of theworking chamber on the underside.

The first side forms a hot side and the second side forms a cold side ofthe flat-plate Stirling engine.

With movement of the displacer, working gas flows through theregenerator. This is embodied or formed such that, when flowed throughwith the working gas, thermal energy contained in the working gas isdelivered or collected.

In the front region of the airfoil profile, i.e., towards the nose edge,a wall running between the top of the wing and the underside of the wingcan be provided, which closes the working chamber with respect to afront region.

The flat-plate Stirling engine can be used for wing statics, i.e.,incorporated in a supporting manner in the support structure of a wing.

The airfoil section can have a leading edge and a trailing edge, inwhich the displacer is held in a pivotable manner in the region of thetrailing edge and in which the displacer forms a plate curved in thedirection of the airfoil profile.

The displacer can include, for example, a fiberboard with heatinsulation property, which has a dark color on the top, e.g., a foamboard.

According to a further embodiment of the invention, the lift device inthe region of the working chamber on the top has a light-transmittingcover in order to render possible a direct heat radiation into theworking chamber.

The cover or the outer skin of the wing device forms a chamber wall inthe region of the working chamber, whereby fewer components result intotal.

According to a further embodiment of the invention, a power-generatingdevice for generating electric energy for driving the aircraft isprovided.

According to a further embodiment of the invention, the power-generatingdevice comprises a generator device for converting kinetic energy intoelectric energy. The generator device can be driven by the flat-plateStirling engine.

The generator device can be detachably coupled with the inertia element.

The generator device can be, for example, a linear generator whichconverts the linear movement of the working piston into electric energy.

According to a further embodiment of the invention, the power-generatingdevice has photovoltaic elements for converting solar radiation intoelectric energy.

According to an embodiment of the invention, the photovoltaic elementsare arranged on the top of the displacer.

The photovoltaic elements can be arranged, for example, in regions onthe top of the aircraft.

According to an embodiment of the invention, the power-generating devicehas a fuel cell device, which feeds the heat released with the operationof a fuel cell to the working chamber of the flat-plate Stirling engine.

According to an embodiment of the invention, a heating device forheating the working gas is provided in one of the two chamber regions ofthe working chamber of the flat-plate Stirling engine.

A support of the flat-plate Stirling engine operation can take place,for example, when the solar heat radiation is present only in a reducedmanner, or the input of the thermal energy of the solar heat radiationcan also be replaced by the heating device, for example, when no solarthermal radiation is present, such as during a night flight, forexample.

The heating device can have, for example, a combustion device operatedwith a fuel. A storage device can be provided to store the fuel.

For example, the fuel used can be obtained from sustainable rawmaterials in order to provide a flight operation that is as CO₂-reducedor CO₂-neutral as possible.

The heating device can have, for example, an electric heating device forconverting electric energy into thermal energy.

According to an embodiment of the invention, the heating device has anelectric heating device for converting electric energy into thermalenergy. The electric heating device is integrally embodied or formed inthe displacer.

For example, the electric heating device is a heating coil that isarranged in one of the two chamber regions in order to heat the workinggas in this region.

The electric heating device can be embodied or formed, for example, as aheating surface of the displacer that can be operated electrically.

The storage and delivery of the electric energy by the storage devicecan take place at different phases.

For example, an electric motor is provided, which is connected to thedrive device, and which can be operated with electric energy from thepower-generating device.

According to an embodiment of the invention, a storage device forstoring and delivering the electric energy generated by thepower-generating device is provided. The power-generating device feedselectric energy to the storage device. The storage device stores the fedelectric energy and makes it available for driving the aircraft.

The storage device can deliver the electric energy, for example, to theelectric heating device.

The storage device delivers the electric energy, for example, to anelectric motor, which is connected to the drive device.

According to a further example of the invention, the flat-plate Stirlingengine is combined with photovoltaic elements, which drive an electricmotor in addition to the flat-plate Stirling engine, in order to operatethe drive device with both drive sources.

According to a further example of the invention, the flat-plate Stirlingengine is combined with photovoltaic elements, and with a battery deviceand an electric motor, in order to provide electric energy for operatingthe electric motor for driving the drive device during the nighttimehours, for example.

According to a further example of the invention, the flat-plate Stirlingengine is connected to a generator, which charges a battery device, inorder to operate an electric motor with the stored electric energy, forexample, during nighttime hours, in order to operate the drive device.The electric motor can also at the same time act as the referencedgenerator, for example, or in the reverse operating mode.

According to a further example of the invention, the flat-plate Stirlingengine is provided combined with photovoltaic elements and a battery, aswell as with a heating device, which can be operated with the electricenergy that is stored in the battery.

According to a further exemplary embodiment of the invention, theflat-plate Stirling engine is combined with a generator, in order to beable to charge a battery, with which in turn a heating device can beoperated during the nighttime hours, for example.

According to a further example of the invention, the flat-plate Stirlingengine is embodied or formed combined with a heating device, which isoperated with a fuel, in order for example to support the operation ofthe flat-plate Stirling engine during the day or also to render possiblethe operation of the flat-plate Stirling engine at night at all.

According to a further example of the invention, the flat-plate Stirlingengine is combined with photovoltaic elements with which a heatingdevice is operated, which supports the operation of the flat-plateStirling engine.

For example, the flat-plate Stirling engine (FSM) is provided incombination with the following components:

-   -   FSM+photovoltaic elements+electric motor;    -   FSM+photovoltaic elements+battery+electric motor;    -   FSM+generator+battery, wherein also possible: generator=electric        motor;    -   FSM+photovoltaic elements+battery+electric heating device;    -   FSM+generator+battery+electric heating device;    -   FSM+heating device, operated with fuel;    -   FSM+photovoltaic elements+heating device.

According to a further aspect of the invention, the flat-plate Stirlingengine is combined with the cited elements of energy conversion andenergy storage in order to, for example, temporarily achieve aparticularly high flying speed.

Moreover, according to the invention, a method for driving an aircraftincludes:

a) feeding of solar thermal energy to a flat-plate Stirling engine;

b) conversion of the thermal energy into kinetic energy by theflat-plate Stirling engine; and

c) driving a drive device by the flat-plate Stirling engine.

According to an embodiment of the invention it is provided that:

-   -   i) in a first phase, kinetic energy of the flat-plate Stirling        engine is converted into electric energy and is stored as        electric energy; and    -   ii) in a second phase, the stored electric energy is converted        into thermal energy in an electric heating device and drives the        Stirling engine in order to provide the kinetic energy for        driving the drive device.

The first phase is provided, for example with existing solar thermalradiation and the second phase with reduced or non-existent solarthermal radiation, for example, at night.

According to embodiments, a flat-plate Stirling engine is placed in anaircraft in order to provide the drive energy for generating the thrust.Solar thermal radiation is utilized as an energy source for theoperation of the flat-plate Stirling engine, which represents a heatengine. The flat-plate Stirling engine, due to its possible lightweightdesign, can be connected well to the other boundary conditions of anaircraft, for example, of an airplane. In addition to the parameter ofweight, here in particular the installation space also plays a decisiverole as a second parameter. Since the flat-plate Stirling engine whenoperated with solar thermal radiation should also be exposed to thesolar thermal radiation over as large a surface as possible, theflat-plate Stirling engine can be integrated in the region of theenveloping surfaces pointing upwards. The flat design means only anegligible restriction of the usable volume. For example, the flat-plateStirling engine can be inserted into the upper region of an airplanefuselage without too much installation space being lost therewith in theinterior of, for example, a passenger cabin. A particularly efficientarrangement can be achieved in that the flat-plate Stirling engine isinstalled in the wing or wings in an integrated manner, since the wingsto generate lift always have a wing geometry that inevitably encloses acertain volume. This wing volume, which is used, for example, toaccommodate fuel tanks, can therefore be used for the accommodation of aflat-plate Stirling engine, which replaces the normal operation withfossil fuels such as kerosene. In order to provide an operation of theflat-plate Stirling engine, i.e., an operation of the aircraft, forexample an airplane, even when the solar thermal radiation is reduced oris not even present at all, an embodiment of the invention providesadditional energy sources via energy storage devices in these operatingphases, in order to generate the thrust for the operation of theaircraft. If, for example, the solar energy available during the day isused in the case of the energy storage and, for example, electric energyis stored by photovoltaic elements, an overall emission-free flightoperation can be provided therewith. An emission-free flight operationis likewise possible when a generator is operated in addition to thethrust device by the Stirling engine during the day, in order togenerate electric energy, which then is stored in an energy storagedevice, such as a battery device, for example, in order to provide thisat night in order to generate thermal energy which is then available tothe flat-plate Stirling engine for operation, or also electric energyfor driving the thrust device. A further possibility for ensuring anemission-free operation also lies in that as an additional energysource, for example, for the direct drive of the thrust device, or alsofor supplying thermal energy to the flat-plate Stirling engine, in orderto also be able to operate it at night, sustainable raw materials areprovided or also hydrogen generated by regenerative energy sources,which can be used in the operation of a fuel cell.

Embodiments of the invention are directed to an aircraft with anemission-free drive. The aircraft includes a drive device structured andarranged to generate thrust, a lift device structured and arranged togenerate lift, and a heat engine structured and arranged to convertthermal energy into kinetic energy to drive the drive device. The heatengine includes at least one flat-plate Stirling engine drivable bysolar thermal radiation.

According to embodiments, the lift device can include a wing device withan airfoil section structured and arranged to generate lift, and theflat-plate Stirling engine may be arranged in the wing device.

In accordance with other embodiments of the present invention, theflat-plate Stirling engine may include a working chamber filled with aworking gas and having a top and an underside and a changeable workingvolume, a displacer structured and arranged to be moveable in theworking chamber between the top and the underside, a regeneratorstructured and arranged in the working chamber to collect and deliverthermal energy contained in the working gas, a working piston connectedto change a working volume of the working chamber, an inertia elementstructured and arranged in a rotatable manner, a drive structured andarranged to be connectable to the inertia element to drive the drivedevice, and a transmission device structured and arranged tomechanically couple the displacer and the working piston with theinertia element. The working chamber can be located in the lift deviceand the working gas may be heatable from a top of the lift device by thesolar thermal radiation. The displacer may be structured and arranged todivide the working chamber into a first and a second chamber region and,with movement, to displace the working gas from one of the first andsecond chamber region into the other of the first and second chamberregion. A top of the wing can form a first side of the flat-plateStirling engine with a first temperature and the underside of the wingcan form a second side of the flat-plate Stirling engine with a secondtemperature. The second temperature may be lower than the firsttemperature. Further, a heating device may be structured and arranged toheat the working gas in one of the first and second chamber regions ofthe working chamber. The heating device can include an electric heatingdevice integrally embodied in the displacer that is structured andarranged to convert electric energy into thermal energy. Still further,a light-transmitting cover may be arranged in the lift device in the topregion of the working chamber.

According to further embodiments, a power-generating device can bestructured and arranged to generate electric energy to drive theaircraft. The power-generating device can include a generator devicestructured and arranged to convert kinetic energy into electric energyand to be driven by the flat-plate Stirling engine. The power-generatingdevice may include photovoltaic elements for converting solar radiationinto electric energy. The photovoltaic elements can be arranged on a topof the displacer. The power-generating device can include a fuel celldevice, and heat released with operation of a fuel cell may be fed to aworking chamber of the flat-plate Stirling engine. Further, a storagedevice may be structured and arranged to store and deliver the electricenergy generated by the power-generating device. The power-generatingdevice can be arranged to feed the electric energy to the storage deviceand the storage device can be structured and arranged to store theelectric energy and to make the stored electric energy available fordriving the aircraft.

Embodiments of the instant invention are directed to a method foremission-free driving of an aircraft. The method includes receivingsolar thermal energy by a flat-plate Stirling engine, converting thethermal energy into kinetic energy via the flat-plate Stirling engine,and driving, via the flat-plate Stirling engine, a drive device.

In further embodiments, the method can include, in a first phase,converting kinetic energy of the flat-plate Stirling engine intoelectric energy and storing the electric energy, and in a second phase,converting the stored electric energy into thermal energy in an electricheating device, and driving the Stirling engine to provide the kineticenergy for driving the drive device.

Embodiments of the invention are directed to an aircraft with at leastone heat engine arranged in at least one of a wing and a fuselage. Theaircraft includes a working chamber, having a top and an undersidefilled with a working gas, being located in the at least of the wing andfuselage, a displacer structured and arranged for movement between thetop and the underside of the working chamber to a define a first and asecond chamber region, and a heating region located in a region of thetop of the working chamber to receive solar thermal radiation throughthe at least one of the wing and fuselage to heat the working gas.

According to embodiments of the invention, the heat engine may include aflat-plate Stirling engine.

In accordance with other embodiments of the invention, the aircraft canfurther include a regenerator structured and arranged in the workingchamber to collect and deliver thermal energy contained in the workinggas, a rotatable inertia element, and a driver structured and arrangedto be connectable to the rotatable inertia element to drive a thrustdrive.

According to still other embodiments, the aircraft may include anelectric heating device one of integral with and coupled to thedisplacer to heat the working gas.

In accordance with still yet other embodiments of the present invention,a storage device may be structured and arranged to store and deliverelectric energy generated by a power-generating device coupled to theheat engine to convert kinetic energy into electric energy.

Other exemplary embodiments and advantages of the present invention maybe ascertained by reviewing the present disclosure and the accompanyingdrawing.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is further described in the detailed descriptionwhich follows, in reference to the noted plurality of drawings by way ofnon-limiting examples of exemplary embodiments of the present invention,in which like reference numerals represent similar parts throughout theseveral views of the drawings, and wherein:

FIG. 1 illustrates an aircraft with an emission-free drive according toan exemplary embodiment of the invention,

FIG. 2 illustrates a further exemplary embodiment of an aircraftaccording to the invention;

FIG. 3 illustrates a diagrammatic section through a wing device of anaircraft according to an exemplary embodiment of the invention;

FIG. 4 illustrates a further exemplary embodiment of an aircraftaccording to the invention;

FIG. 5 illustrates a vertical section through a further exemplaryembodiment of a wing device according to the invention;

FIG. 6 illustrates a further exemplary embodiment of an aircraftaccording to the invention;

FIG. 7 illustrates a vertical section through a further exemplaryembodiment of a wing device according to the invention;

FIG. 8 illustrates a vertical section through a further exemplaryembodiment of a wing device according to the invention;

FIG. 9 illustrates a further exemplary embodiment of a wing device invertical section with a heating device according to the invention;

FIG. 10 illustrates a further exemplary embodiment of a wing device invertical section with a further example of a heating device according tothe invention;

FIG. 11 illustrates a further exemplary embodiment of a wing deviceaccording to the invention in vertical section;

FIG. 12 illustrates a further exemplary embodiment of a wing device invertical section according to the invention with a storage device forstoring and delivering electric energy;

FIG. 13 illustrates process steps of a method according to the inventionfor driving an aircraft according to an exemplary embodiment of theinvention;

FIG. 14 illustrates a further example of a method according to theinvention; and

FIG. 15 illustrates a displacer with an integrally formed heatingdevice.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The particulars shown herein are by way of example and for purposes ofillustrative discussion of the embodiments of the present invention onlyand are presented in the cause of providing what is believed to be themost useful and readily understood description of the principles andconceptual aspects of the present invention. In this regard, no attemptis made to show structural details of the present invention in moredetail than is necessary for the fundamental understanding of thepresent invention, the description taken with the drawings makingapparent to those skilled in the art how the several forms of thepresent invention may be embodied or formed in practice.

FIG. 1 shows a first example of an aircraft 10 with an emission-freedrive 12, which is explained in more detail in the following figures.The aircraft 10 has a drive device 14 for generating a thrust, forexample in the form of two propeller devices 16, 18. Moreover theaircraft 10 has a lift device 20 for generating a lift, for example, inthe form of two lateral wings 22, 24.

Furthermore, a heat engine 26, not shown in detail, is provided forconverting thermal energy into kinetic energy for driving the drivedevice. To this end, according to the present embodiments of theinvention, at least one flat-plate Stirling engine 28 is provided as amotor, which can be driven by solar thermal radiation (not shown in FIG.1).

The aircraft is, for example, an airplane, particularly manned andunmanned airplanes can be provided. Moreover, in addition to anairplane, embodiments of the invention include airships, which are,however, not shown in detail.

FIG. 1 shows by way of example an aircraft 10, e.g., a manned aircraft,that has diagrammatically an airplane tip 30 and a tail region 32. Atailplane 34 and an elevator unit 36 are indicated in the tail region32. A dashed line 38 designates a longitudinal axis of the airplane, anda direction arrow 40 shows the flight direction.

FIG. 2 shows a further exemplary embodiment in which, instead of the twopropeller devices 16, 18, a propeller device 41 provided in the regionof the airplane tip 30 is shown.

Naturally, a larger number of propeller devices can also be provided.For example, the propeller device 41 can be combined with the twopropeller devices 16, 18 or with two or more propeller devices along thewings. Moreover, more than two propellers 16, 18 can be arranged alongthe wings without propeller 41.

The flat-plate Stirling engine 28 can be embodied or formed, forexample, in an upper region of the fuselage construction, as is shownwith a dashed line 43 in FIG. 2, in order to drive via a connection 42,the center propeller of the propeller device 41.

Alternatively or additionally, in FIG. 1 it is indicated by a dashedline 44 that the flat-plate Stirling engine 28 is integrated into thelift device 20. In other words, the lift device 20, which comprises awing device 46 with an airfoil section 48 for generating a lift, servesto accommodate the at least one flat-plate Stirling engine 28.

The flat-plate Stirling engine 28 is explained in more detail withreference to FIG. 3, in which the flat-plate Stirling engine 28 is shownaccommodated in the wing device 46. However, it is understood that theflat-plate Stirling engine 28 can also be provided at other locations,such as, e.g., in the upper fuselage region or also in the front regionof the airplane.

The flat-plate Stirling engine 28 has a working chamber 52 filled with aworking gas 50, and includes a top 54 and an underside 56 and achangeable working volume 58. Moreover, a displacer 60 is held in theworking chamber 52 in a moveable manner between the top 54 and theunderside 56. Furthermore, a regenerator 62 is arranged in the workingchamber 52 for collecting and delivering thermal energy contained in theworking gas 50. Furthermore, a working piston 64 is connected to theworking chamber 52. The working piston 64 is used to change the workingvolume 58. Furthermore, an inertia element 66 is held in a rotatablemanner, and an output 68 is connected to the inertia element 66 fordriving the drive device, for example, the propeller 16 or 18 and/or 41.Moreover, a transmission device 70 mechanically couples the displacer 60and the working piston 64 to the inertia element 66. The working chamber52 is arranged in the lift device and the working gas 50 can be heatedby solar thermal radiation, indicated symbolically by arrows 74, from atop 72 of the lift device.

The transmission device 70 has a first push rod connection 75 whichcouples the displacer 60 at a first pivot point 76 of the inertiaelement 66. Moreover, the transmission device 70 has a second push rodconnection 78, which couples the working piston 64 at a second pivotpoint 80 of the inertia element 66. The first pivot point 76 on theinertia element 66 is arranged offset by 90° in its rotation angleposition in a rotation direction 82 in front of the second pivot point76.

The working piston 64 is held in a moveable manner in a working cavity84 and forms a moveable wall surface of the working chamber 52.

As indicated diagrammatically in FIG. 3, the working chamber 52 isembodied or formed between a top of a wing 86 and an underside of a wing88. The displacer 60 divides the working chamber 52 into a first, i.e.,upper chamber region and a second, i.e., lower chamber region. Thedisplacer 60 is thereby embodied or formed so that with movement about apivot point 90, working gas 50 is displaced from the one chamber regioninto the other chamber region. The top of the wing 86 thereby forms afirst side of the flat-plate Stirling engine 28 with a firsttemperature, and the underside of the wing 88 forms a second side of theflat-plate Stirling engine 28 with a second temperature. The secondtemperature is lower than the first temperature.

For example, an aluminum sheet can be provided on the underside 88 forcooling.

With movement of the displacer 60, working gas 50 flows through theregenerator 62, which is sealed to the front region of the wing cavityby a bulkhead 92. The bulkhead 92 forms a wall running between the topof the wing and the underside of the wing which closes the workingchamber 52 with respect to the front region.

The flat-plate Stirling engine 28 can be embodied or formed, forexample, between adjacent rib constructions of the wing, and thebulkhead 92 can be embodied or formed in connection with an airfoilsection running in the longitudinal direction. The flat-plate Stirlingengine 28 can be used, for example, for wing statics or be integratedinto the support structure concept. According to embodiments, severalflat-plate Stirling engines can also be embodied or formed in thelongitudinal direction of the wing, which runs transversely to theactual flight direction, i.e., the longitudinal axis 38 of the airplane.

The displacer 60 can in particular be embodied or formed as a plate bentin the direction of the airfoil profile, in order to be able tooptimally utilize the wing geometry.

The displacer 60 can be formed from or include, for example, afiberboard with at least one thermal insulation property, having top adark color on a top surface, e.g., a foam board painted black. Asufficiently stable board material can be provided, which also includesonly a very low weight. The provision of a dark color on the topsupports the heating up of the working gas 50 in the upper region, i.e.,the upper chamber.

To this end, for example, the lift device in the region of the workingchamber 52 on the top can have a light-transmitting cover 94. Thelight-transmitting cover 94 can be embodied or formed thereby, forexample, in a transparent or also translucent manner, the importantfactor is that sufficient thermal radiation can enter the region of theworking chamber 52. For example, shortwave solar radiation can enter theregion in order to be converted there into longwave thermal radiation.

The cover or exterior skin of the wing device can thereby also at thesame time form the chamber wall in the region of the working chamber 52.

As shown in FIG. 4, a further exemplary embodiment is directed to apower-generating device 96 that is diagrammatically illustrated in FIG.4, and can be provided for generating electric energy for driving theaircraft.

For example, as shown in FIG. 5, the power-generating device 96 cancomprise a generator device 98 for converting kinetic energy intoelectric energy. The generator device 98 is driven by the flat-plateStirling engine 28.

At this point it should be noted that the connection of the inertiaelement 66 to the drive device, i.e., the propeller, as well as theconnection to the generator device 98 are shown merely diagrammaticallyas a type of bevel gear connection. Of course, other transmissionconnection mechanisms can also be used here.

According to a further exemplary embodiment, the power-generating device96 can have photovoltaic elements 100 for converting solar radiationinto electric energy. FIG. 6 shows, for example, that the photovoltaicelements 100 can be arranged in the region of the roof construction 102or in the region of the front airplane tip 104 and/or also in the regionof the wings 106.

According to a further exemplary embodiment, which is shown in FIG. 7,the photovoltaic elements are arranged on the top of the displacer,which is indicated by a double line 108.

The power-generating device 96 according to a further exemplaryembodiment can also have a fuel cell device 110, for example,accommodated inside the fuselage construction, as is indicateddiagrammatically in FIG. 4. The fuel cell device 110 can also bearranged inside a wing construction, as is shown in FIG. 8. It canthereby also be provided, for example, that the heat released with afuel cell operation is fed to the working chamber of the flat-plateStirling engine (not shown in further detail in FIG. 8).

According to a further exemplary embodiment, a heating device 112 forheating the working gas is provided in one of the two chamber regions ofthe working chamber of the flat-plate Stirling engine, i.e., in thehotter region of the working chamber.

For example, the heating device 112 can have an electric heating device114 for converting electric energy into thermal energy. The electricheating device 114 is attached to the displacer 60, as is shown in FIG.9, or the electric heating device 114 is embodied or formed, forexample, integrally in the displacer 60, as is shown by the dashed linesin FIG. 15. The heating device 114 can be a heating coil, for example,as is indicated in FIG. 9 or as a resistance layer, not shown in detail,on the displacer 60, which produces heat inside the working chamber byelectric energy.

According to a further exemplary embodiment of the invention, which isshown in FIG. 10, the heating device can have a combustion device 116operated with a fuel. Additionally, a storage device 118 is provided tostore the fuel. The combustion device 116 can be provided in theimmediate vicinity of the flat-plate Stirling engine 28, as is indicatedin FIG. 10, or at a different location, however, for example, inside thefuselage construction, in order to transport the heat from there to theflat-plate Stirling engine 28 (not shown in detail).

According to the exemplary embodiment shown in FIG. 11, an electricmotor 120 connected to the drive device, for example, the propellerdevice 16, 18 and/or 41 and can be operated with electric energy of thepower-generating device (not shown in detail in FIG. 11).

FIG. 12 shows a further exemplary embodiment in which a storage device122 for storing and delivering the electric energy generated by thepower-generating device 96 is provided. The power-generating device 96feeds electric energy to the storage device 122 and the storage device122 stores the fed electric energy and provides this for operating theaircraft.

FIG. 12 shows that the storage device 122, for example, is provided as abattery pack which can be accommodated at different locations inside thewing or also inside the fuselage construction (not shown in detail), asis indicated merely by way of example for a first position 124 and asecond position 126.

The storage device 122, for example, delivers the electric energy to theelectric heating device 114. The storage and the delivery of theelectric energy by the storage device can thereby take place atdifferent phases.

The storage device 122 can also however, additionally or alternatively,deliver the electric energy to an electric motor, for example, theelectric motor 120, which is connected to the drive device.

According to an embodiment variant of the aircraft, the flat-plateStirling engine 28 is embodied or formed with the photovoltaic elements100, with which the electric motor 120 can be operated to support theflat-plate Stirling engine 28. It should be noted that this embodimentvariant as well as the embodiment variants shown below are notrepresented, but the described combinations are understandable for theperson skilled in the art from the above described representations ofthe individual components.

According to a further embodiment variant, the flat-plate Stirlingengine 28 is combined with the photovoltaic elements 100 that deliverthe electric current, which can be generated by the solar insolationduring the day, to the battery and/or several batteries, i.e., theelectric storage device 122, in order to generate a thrust with theelectric motor 120 for times when solar thermal radiation is notavailable to the flat-plate Stirling engine 28.

According to a further embodiment variant, the flat-plate Stirlingengine 28 is combined with the generator device 98, in order to conductcurrent to the storage device 122 during the day, in order subsequentlyto be able to operate the aircraft even in the dark by the electricmotor 120. The generator 98 can be embodied or formed integrated withthe electric motor 120, i.e., to put it simply, the electric motor 120can also be used in the reverse direction as a generator.

According to a further embodiment variant, the flat-plate Stirlingengine 28 is combined with the photovoltaic elements 100, and with thebattery or the storage device 122. Moreover, the electric heating device114 is provided, in order thus, for example, to feed thermal energy atnight to the flat-plate Stirling engine 28, in order to be able tooperate the drive device 14 with the flat-plate Stirling engine 28.

According to a further embodiment variant, the flat-plate Stirlingengine 28 is combined with the generator or the generator device 98 andthe storage device 122. The stored current can then be fed at night tothe electric heating device 114 in order to operate the drive device 14.The embodiment of the generator is thereby in particular advantageous,which can be embodied or formed to be much smaller and lighter comparedto an electric motor for driving the drive device.

According to a further embodiment variant, the flat-plate Stirlingengine 28 is combined with the heating device or the combustion device116, by which thermal energy can be generated during nighttime hours,and is fed to the flat-plate Stirling engine 28 in order to operate thedrive device 14 therewith.

According to a further embodiment variant, the flat-plate Stirlingengine 28 is combined with the photovoltaic elements 100, which operatethe electric heating device 114 during the day in order to makeadditional heat available to the flat-plate Stirling engine 28 inaddition to the solar thermal radiation. Due to the combination with thephotovoltaic elements, the surface of the airplane, which is exposed tothe solar insolation, or the thermal radiation can be used optimally andnot only those regions that are arranged immediately above theflat-plate Stirling engine working chamber.

Of course, the embodiment variants described above can also be combinedwith one another in order to thus to make available overall the bestpossible utilization of the drive concept of the flat-plate Stirlingengine 28.

Finally FIG. 13 shows a further exemplary embodiment of a method 200 fordriving an aircraft, which comprises the following steps: in a firststep 210, solar thermal energy is fed to a flat-plate Stirling enginewhich is provided in the aircraft as a heat engine, in order to drive adrive device to generate a thrust. In a second step 212, the thermalenergy is converted by the flat-plate Stirling engine into kineticenergy. In a third step 214, a driving of the drive device by theflat-plate Stirling engine takes place.

The first step 210 is also referred to as step a), the second step 212as step b) and the third step 214 as step c). The steps a), b) and c)naturally take place at the same time in a continuous manner during theoperation of the aircraft.

According to a further exemplary embodiment, which is shown in FIG. 14,in a first phase, kinetic energy of the flat-plate Stirling engine isconverted into electric energy in a conversion operation 216 and isstored as electric energy. In a second phase, the stored electric energyis converted into thermal energy in a second conversion step 218 andthereby drives the Stirling engine in order to make available thekinetic energy for driving the driving device.

The first phase is also referred to as step i) and the second phase asstep ii). The first phase is provided, for example, with existing solarthermal radiation and the second phase with reduced or unavailable solarthermal radiation, for example at night. The storage and delivery of theelectric energy by the storage device thus takes place at differentphases, for example, which is why the connection arrows of the firstconversion step 216 and the second conversion step 218 are shown bydashed lines in each case.

According to a further exemplary embodiment, but not shown in detail, itis provided with the method that the kinetic energy is converted intoelectric energy by the generator mentioned above. Additionally oralternatively, the electric energy can also be made available, forexample, by photovoltaic elements or also by a fuel cell, as wasexplained above based on the different device variants, which is why anexplicit representation of corresponding method diagrams is omitted.

According to a further aspect of the invention, due to the combinationof the flat-plate Stirling engine with an additional generation ofelectric energy during the day and the delivery of the electric energyand subsequent conversion into thermal energy at night, an airplane ispossible that flies permanently or in an unlimited manner, which derivesits drive from solar heat. In addition to the solar insolation duringthe day for the Stirling engine, at night as it were an alternativeenergy source is provided, which can be stored during the day to beavailable at night. To this end the heat is converted into movement fromthe heat engine in the form of the Stirling engine and the movement isconverted into current by a generator. A battery can therefore store theexcess energy during the day in order to convert it at night into heatagain and to thereby drive the heat engine in the form of the flat-plateStirling engine. In particular, the high efficiency of the flat-plateStirling engine with the utilization of the thermal energy and the highyield of the electric energy with the generation of thermal energy is tobe noted, which overall ensures high efficiency.

The exemplary embodiments described above can be combined in differentways.

In addition it should be noted that “comprising” does not exclude anyother elements or steps and “one” does not exclude a plural.Furthermore, it should be noted that features or steps that have beendescribed with reference to one of the above exemplary embodiments canalso be used in combination with other features or steps of otherexemplary embodiments described above.

It is noted that the foregoing examples have been provided merely forthe purpose of explanation and are in no way to be construed as limitingof the present invention. While the present invention has been describedwith reference to an exemplary embodiment, it is understood that thewords which have been used herein are words of description andillustration, rather than words of limitation. Changes may be made,within the purview of the appended claims, as presently stated and asamended, without departing from the scope and spirit of the presentinvention in its aspects. Although the present invention has beendescribed herein with reference to particular means, materials andembodiments, the present invention is not intended to be limited to theparticulars disclosed herein; rather, the present invention extends toall functionally equivalent structures, methods and uses, such as arewithin the scope of the appended claims.

What is claimed:
 1. An aircraft with an emission-free drive, comprising:an aircraft thruster structured and arranged to generate thrust; anaircraft lift device structured and arranged to generate lift; and aheat engine, which is structured and arranged to convert thermal energyinto kinetic energy to drive the aircraft thruster, comprising at leastone flat-plate Stirling engine drivable by solar thermal radiation. 2.The aircraft according to claim 1, wherein the aircraft lift devicecomprises a wing with an airfoil section structured and arranged togenerate lift, and the flat-plate Stirling engine is arranged in thewing.
 3. The aircraft according to claim 1, the flat-plate Stirlingengine comprising: a working chamber filled with a working gas andhaving a top and an underside and a changeable working volume; adisplacer structured and arranged to be moveable in the working chamberbetween the top and the underside; a regenerator structured and arrangedin the working chamber to collect and deliver thermal energy containedin the working gas; a working piston connected to change a workingvolume of the working chamber; an inertia element structured andarranged in a rotatable manner; a drive structured and arranged to beconnectable to the inertia element to drive the aircraft thruster; and atransmission structured and arranged to mechanically couple thedisplacer and the working piston with the inertia element, wherein theworking chamber is located in the aircraft lift device and the workinggas is heatable from a top of the aircraft lift device by the solarthermal radiation.
 4. The aircraft according to claim 3, furthercomprising a light-transmitting cover arranged in the aircraft liftdevice in the top region of the working chamber.
 5. The aircraftaccording to claim 1, further comprising a power-generator structuredand arranged to generate electric energy to drive the aircraft.
 6. Theaircraft according to claim 5, the power-generator comprising agenerator device structured and arranged to convert kinetic energy intoelectric energy and to be driven by the flat-plate Stirling engine. 7.The aircraft according to claim 5, the power-generator comprisingphotovoltaic elements for converting solar radiation into electricenergy.
 8. The aircraft according to claim 5, the power-generatorcomprising a fuel cell device; and heat released with operation of afuel cell being fed to a working chamber of the flat-plate Stirlingengine.
 9. The aircraft according to claim 5, further comprising astorage device structured and arranged to store and deliver the electricenergy generated by the power-generator, wherein the power-generator isarranged to feed the electric energy to the storage device and thestorage device is structured and arranged to store the electric energyand to make the stored electric energy available for driving theaircraft.
 10. A method for emission-free driving of an aircraft,comprising: receiving solar thermal energy by a flat-plate Stirlingengine; converting the thermal energy into kinetic energy via theflat-plate Stirling engine; and driving, via the flat-plate Stirlingengine, an aircraft thruster.
 11. The method according to claim 10,wherein: in a first phase, converting kinetic energy of the flat-plateStirling engine into electric energy and storing the electric energy;and in a second phase, converting the stored electric energy intothermal energy in an electric heater, and driving the Stirling engine toprovide the kinetic energy for driving the aircraft thruster.
 12. Anaircraft with at least one heat engine, the aircraft comprising: a wingand a fuselage; a working chamber of the at least one heat engine,having a top and an underside filled with a working gas, being locatedin at least one of the wing and fuselage; a displacer of the at leastone heat engine being structured and arranged for movement between thetop and the underside of the working chamber to a define a first and asecond chamber region; and a heating region of the at least one heatengine being located in a region of the top of the working chamber toreceive solar thermal radiation through the at least one of the wing andfuselage to heat the working gas.
 13. The aircraft according to claim12, the heat engine comprising a flat-plate Stirling engine.
 14. Theaircraft according to claim 12, further comprising: a regenerator of theat least one heat engine being structured and arranged in the workingchamber to collect and deliver thermal energy contained in the workinggas; a rotatable inertia element of the at least one heat engine being;and a driver of the at least one heat engine being structured andarranged to be connectable to the rotatable inertia element to drive athrust drive.
 15. The aircraft according to claim 12, further comprisinga storage device structured and arranged to store and deliver electricenergy generated by a power-generator coupled to the heat engine toconvert kinetic energy into electric energy.